Tumour necrosis factor α blockade induces an anti‐inflammatory growth hormone signalling pathway in experimental colitis

X Han

N Benight

B Osuntokun

K Loesch

S Frank

L Denson

K Loesch, S J Frank, Department of Cell Biology, University of Alabama at Birmingham, Alabama, USA

Correspondence to: Dr L A Denson
MLC 2010, 3333 Burnet Avenue, Cincinnati, OH 45229‐3039, USA; lee.denson@cchmc.org

X Han, N Benight, B Osuntokun, L A Denson, Department of Pediatrics, Cincinnati Children's Hospital Medical Center and the University of Cincinnati College of Medicine, Cincinnati, Ohio, USAK Loesch, S J Frank, Department of Cell Biology, University of Alabama at Birmingham, Alabama, USACorrespondence to: Dr L A Denson
MLC 2010, 3333 Burnet Avenue, Cincinnati, OH 45229‐3039, USA; lee.denson@cchmc.org

Revised 2006 Apr 22; Accepted 2006 Jun 8.

Abstract

Background

Neutralisation of tumour necrosis factor α (TNFα)restores systemic growth hormone function in patients with Crohn's disease, and induces mucosal healing. Anabolic effects of growth hormone depend on activation of the STAT5 transcription factor. Although it has recently been reported that both administration of growth hormone and neutralisation of TNFα reduce mucosal inflammation in experimental colitis, whether this involved activation of STAT5 in the gut is not known.

Aim

To determine whether TNFα blockade in colitis up regulates a growth hormone:STAT5 signalling pathway in the colon.

Methods

Interleukin 10‐deficient mice and wild‐type controls received growth hormone or anti‐TNFα antibody, and T84 human colon carcinoma cells were treated with TNFα or growth hormone. Activation and expression of STAT5b, peroxisome proliferator‐activated receptor gamma (PPARγ), NFκB/IκB and growth hormone receptor were determined.

Results

Growth hormone activated STAT5b and up regulated expression of PPARγ in normal mouse colon; inflamed colon was partially resistant to this. Chronic administration of growth hormone, nevertheless, significantly reduced activation of colonic NFκB (p = 0.028). Neutralisation of TNFα rapidly increased abundance of growth hormone receptor, activation of STAT5 and abundance of PPARγ in the colon, but reduced activation of NFκB in colitis. Growth hormone activated STAT5, and directly reduced TNFα activation of NFκB, in T84 cells.

Conclusions

Reduced activation of colonic STAT5 and expression of PPARγ may contribute to persistent mucosal inflammation in colitis. Up regulation of STAT5 and PPARγ, either through neutralisation of TNFα or chronic administration of growth hormone, may exert an anti‐inflammatory effect in inflammatory bowel disease.

Abstract

Patients with Crohn's disease exhibit hepatic resistance to the action of growth hormone, manifested by low circulating levels of insulin‐like growth factor 1 (IGF1) despite adequate central growth hormone secretion.¹ This contributes to cachexia, reduced bone mineral density and linear growth failure. Administration of the monoclonal anti‐tumour necrosis factor α (TNFα) antibody, infliximab, restores normal circulating levels of IGF1 within 24 h, consistent with restoration of growth hormone signalling in the liver.²³ This leads to improvements in growth and bone mineral density over time.⁴ Our group recently reported that expression of growth hormone receptor (GHR) and activation of growth hormone‐dependent STAT5b in the liver are reduced in interleukin 10 (IL10)‐deficient mice with colitis, providing a molecular basis for the hepatic resistance to growth hormone that is observed in patients. TNFα neutralisation up regulated abundance of GHR in the liver and activation of growth hormone‐dependent STAT5b and serum IGF1 within 24 h, mimicking the results observed in patients with Crohn's disease.⁵ However, whether activation of STAT5 in the affected colon would similarly increase after TNFα blockade in colitis is not known.

Administration of growth hormone reduces mucosal inflammation in several animal models of colitis, and alleviates symptoms in patients with Crohn's disease.⁶⁷⁸⁹ The GHR is expressed on epithelial and lamina propria cells of the small bowel and colon.¹⁰ However, regulation of growth hormone signalling in the normal or inflamed gut is not well understood. Although there are several intracellular targets for growth hormone signalling in the liver, activation of STAT5b has been shown to regulate expression of IGF1 and linear growth in a non‐redundant manner.¹¹ Recently, growth hormone has also been shown to up regulate the peroxisome proliferator‐activated receptor gamma (PPARγ) 3 isoform in humans, in a manner that involves STAT5b but not STAT5a.¹² The PPARγ3 isoform is expressed in colon epithelial cells (CECs) and macrophages, and would be expected to exert a tolerigenic effect in colitis through local inhibition of activation of nuclear factor κB (NFκB).¹³¹⁴¹⁵¹⁶¹⁷¹⁸ Conversely, targeted deletion of both STAT5a and STAT5b is required to produce spontaneous autoimmune disease, including colitis in mice, through decreased survival of regulatory T cells.¹⁹ As growth hormone activates both STAT5a and STAT5b, this raises the possibility that growth hormone signalling might exert a tolerigenic effect in the gut under normal conditions, and that a TNFα‐dependent reduction in growth hormone function might promote chronic mucosal inflammation.

The monoclonal anti‐TNFα antibody infliximab can considerably reduce mucosal inflammation in Crohn's disease; this has been attributed to apoptosis of lamina propria effector T cells.²⁰²¹²²²³²⁴²⁵ However, neutralisation of TNFα may also restore an endogenous tolerigenic pathway in the gut. We hypothesised that neutralisation of TNFα would rapidly restore a novel growth hormone‐dependent anti‐inflammatory pathway in the colon, comprised of activation of STAT5b and nuclear expression of PPARγ, thereby contributing to mucosal healing. In this study, we determined that neutralisation of TNFα rapidly increases activation of STAT5 and nuclear abundance of PPARγ in the colon of mice with chronic colitis owing to IL10 deficiency, leading to reduced activation of NFκB.

Acknowledgements

Mouse colon sections for histological analysis were prepared in the Integrative Morphology Core of the National Institutes of Health (NIH)‐supported Children's Hospital Research Foundation Digestive Diseases Research and Development Center (R24 DK64403).

Acknowledgements

Abbreviations

CEC - colon epithelial cells

EMSA - electrophoteric mobility shift assay

GHR - growth hormone receptor

GM‐CSF - granulocyte‐macrophage colony‐stimulating factor

IGF1 - insulin‐like growth factor 1

IHC - immunohistochemistry

LPMC - lamina propria mononuclear cells

NFκB - nuclear factor κB

PBS - phosphate‐buffered saline

PCR - polymerase chain reaction

PPARγ - peroxisome proliferator‐activated receptor gamma

TNF - tumour necrosis factor

Abbreviations

Footnotes

Funding: This work was supported by NIH grants DK02700, DK63956 and DK068164 (LAD), as well as the Crohns and Colitis Foundation of America (XH), the Cincinnati Children's Hospital Research Foundation, the Children's Digestive Health Foundation/Nestle Nutrition, the Broad Medical Research Program (LAD) and NIH grant R01 DK058259 (SJK).

Competing interests: LAD has received research support from Centocor, which provided the rat/mouse monoclonal anti‐TNFα antibody (clone cV1q) and isotype control immunoglobulin G antibody (cVaM).

Footnotes

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